The invention relates to noise reduction in a gas turbine and, more particularly, to the use of a multiple stage ejector/mixer nozzle in a gas turbine inlet bleed heat application to reduce noise.
The combustion system of a gas turbine generates hot gases to drive a turbine. The turbine, in turn, drives a compressor that provides compressed air for combustion in the combustion system. The turbine produces usable output power.
In some gas turbine applications, there are instances of gas turbine plant operation where the gas turbine pressure ratio reaches the operating pressure ratio limit of the compressor, resulting in compressor surge. These instances may arise in applications where low BTU fuels or any other fuels with large amounts of diluent injection are used and/or at cold ambient temperature conditions. The compressor pressure ratio is typically larger than the turbine pressure ratio in that the latter is subject to pressure loss in the turbine combustor.
One common solution that has been used to provide compressor pressure ratio protection is the bleeding off of gas turbine compressor discharge air and recirculating the bleed air back to the compressor inlet. This method of gas turbine operation, known as Inlet Bleed Heat (IBH) Control, raises the inlet temperature of the compressor inlet air by mixing the colder ambient air with the bleed portion of the hot compressor discharge air, thereby reducing the air density and the mass flow to the gas turbine.
When a gas turbine bleeds compressor air into the inlet duct, it creates noise that can exceed noise limits. Existing designs place the bleeding manifolds downstream of inlet silencing panels. This arrangement can address an icing problem of the compressor IGV, but does not sufficiently solve the problem of inlet filter housing icing. If the bleeding manifolds are placed before the silencers in the inlet duct to address the icing problem, the noise problem arises.
A silencing nozzle was proposed for an IBH system. Silencing nozzles, however, are expensive. A related problem has been addressed in aircraft engine technology, using an ejector/mixer nozzle to reduce aircraft engine noise. The noise results from shearing action between the surrounding atmosphere and air jets from orifices. After a multi-stage ejector/mixer, the jet velocity is slowed down significantly, thereby reducing noise. There is currently no similar technology to reduce noise in a gas turbine.
It would thus be desirable for an IBH system to include an ejector/mixer noise reduction nozzle to enhance the mixing of hot air in the turbine without the use of expensive components.